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I recently lapped a paddle strop on a belt sander and then buffed it with an almost-clean wheel (to prevent buffing paste to cover the leather). It worked well and the leather is very smooth.

You should not use any pressure, nor feel a bumpy surface.

The bumps can either be the result of bad glueing or bumpy paddle or leather. If you glued bubbles, try glueing again using a dough...

Crox on balsa is a commonly used combination. As for the leather, you can go quite a few ways there. I think it depends on your finishing hone, going from an 8K hone to a 0.25 micron diamond spray...